The invention relates to loudspeakers and to low-cost magnetic motors for use in loudspeakers. The invention has application, among other places, in cell phones, pagers, MP3 players, and other appliances where weight and size are factors.
A large percentage of loudspeakers are electrodynamic speakers. Such speakers employ a magnetic driver to produce movement of a diaphragm (typically cone or dome-shaped) which, in turn, causes sound. A typical loudspeaker includes a fixed magnet and voice coil. The magnet may be mounted to the rear of the frame behind the diaphragm. A magnetic “circuit” may be utilized to focus and, therefore, intensify the magnetic field in a region referred to as the “air gap”. The voice coil is disposed adjacent the magnet and, preferably, within the air gap. The coil typically wire formed about a cylindrical support or “former” which, itself, is attached to the diaphragm.
In operation, electrical audio signals from an amplifier are applied to the voice coil producing a varying electromagnetic field around the coil. The electromagnetic field interacts with the magnetic field produced by the magnet. The magnet is securely fixed to the frame and the voice coil is movable, so the voice coil moves as the two fields interact. Because the voice coil is coupled to the diaphragm via the support, its movement causes the diaphragm to vibrate. The vibration of the diaphragm causes air around the speaker to pressurize and depressurize producing sound waves in the air.
The high energy density of rare earth materials such as neodymium boron iron is attractive for creating and miniaturizing shielded loudspeaker magnets. The magnet rings or discs can best be installed as cores on the inside of the transducers voice coil for easy manufacturing. The maximum storable and extractable energy is then limited by the voice coil diameter and can be increased only by the height of the neodymium slug.
An object of this invention is to provide improved loudspeakers and, more particularly, improved magnetic motors for loudspeakers.
A further object of the invention is to provide such motors that utilize rare earth magnets.
A still further object of the invention is to provide such motors as permit construction of lower impedance, higher B×L neodymium motors for driving loudspeakers.
Yet a still further object is to provide such motors as eliminate the need for multiple magnets and expensive edge winding and offers greater freedom in amplifier matching for best overall system value.
Still yet further objects of the invention are to provide such motors as permit the construction of low voltage sound systems for portable talking appliances like cell phones, note book and palm size computers, pagers, and other interactive wireless appliances.